1. Field of the Invention
The present invention relates to a navigation system and a navigation method, and more particularly to a navigation system and a navigation method capable of changing input frame selection period based on movement speed of an optical mouse, wherein pixel mapping is performed by comparing all the pixels in a current input frame with all the pixels in a reference frame.
2. Description of the Related Art
The operation of an optical mouse is will be described below with reference to FIG. 1. Referring to FIG. 1, light beams 7 emitted from an illuminating source 8 are incident onto a worktable and are reflected at the surface 2 of the worktable. The reflected light beams 6 pass through a lens 5 and are incident onto an optical sensor implemented by a semiconductor chip. The optical sensor 3 continuously captures images formed on the surface of the worktable and then the captured images are stored in a memory device (not shown). A currently captured image (a current input image) and a precedently captured image (a preceding input image) stored in the memory device are compared with each other and correlation values therebetween are obtained. Then, displacement of the optical mouse is calculated with the correlation values and transmitted to a computer system.
A conventional navigation method is disclosed in U.S. Pat. No. 5,644,139, which is issued to Allen et al. under a title “NAVIGATION TECHNIQUE FOR DETECTING MOVEMENT OF NAVIGATION SENSORS RELATIVE TO AN OBJECT”. Referring to FIG. 2, a conventional pixel mapping method for obtaining correlation values between a current input frame and a reference frame will be described below.
First, a reference frame data is obtained, and then a current input frame data is obtained. Then, the correlation values between the reference frame data and the current input frame data are calculated. Each pixel on the reference frame is compared with its corresponding pixel and eight pixels around the corresponding pixel on the current input frame, and it is determined whether the current input frame is moved by one pixel from the reference frame. As a result, in the case that the current input frame is moved from the reference frame by one pixel, displacement with respect to such movement is obtained. Then, a reference frame is newly set by moving the old reference frame to the matched pixel. Since such conventional pixel mapping is targeted to detect movement or displacement within one pixel in nine directions, if an optical mouse moves by more than one pixel in one sampling period, the optical mouse cannot trace the movement of the optical mouse and therefore generates an error. To prevent such a movement trace error, the movement detection is achieved by increasing sampling speed of input frames. However, there is a limitation to increase electrical speed of an optical sensor. This conventional method is disadvantageous in additional power consumption and noise increase.
Further, the conventional method is disadvantageous in that the conventional navigation system consumes a great amount of power and causes a big noise because input frame selection period is maintained constant even if movement speed of an optical mouse is changed.